Programmable power supplies for cellular base stations and related methods of reducing power loss in cellular systems

ABSTRACT

Methods of powering a radio that is mounted on a tower of a cellular base station are provided in which a direct current (“DC”) power signal is provided to the radio over a power cable and a voltage level of the output of the power supply is adjusted so as to provide a substantially constant voltage at a first end of the power cable that is remote from the power supply. Related cellular base stations and programmable power supplies are also provided.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional of and claims priority under 35U.S.C. § 119 to U.S. patent application Ser. No. 14/321,897, filed Jul.2, 2014, which in turn claims priority under 35 U.S.C. § 119 to U.S.Provisional Patent Application Ser. No. 61/940,631, filed Feb. 17, 2014,the entire contents of each of which is incorporated herein by referenceas if set forth in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to cellular communicationssystems and, more particularly, to power supplies for cellular basestations that may exhibit reduced power loss.

BACKGROUND

Cellular base stations typically include, among other things, a radio, abaseband unit, and one or more antennas. The radio receives digitalinformation and control signals from the baseband unit and modulatesthis information into a radio frequency (“RF”) signal that is thentransmitted through the antennas. The radio also receives RF signalsfrom the antenna and demodulates these signals and supplies them to thebaseband unit. The baseband unit processes demodulated signals receivedfrom the radio into a format suitable for transmission over a backhaulcommunications system. The baseband unit also processes signals receivedfrom the backhaul communications system and supplies the processedsignals to the radio. A power supply may also be provided that generatessuitable direct current (“DC”) power signals for powering the basebandunit and the radio. For example, the radio is often powered by a(nominal) 48 Volt DC power supply in cellular systems that are currentlyin use today. A battery backup is also typically provided to maintainservice for some period of time during power outages.

In order to increase coverage and signal quality, the antennas in manycellular base stations are located at the top of a tower, which may be,for example, about fifty to two hundred feet tall. Until fairlyrecently, the power supply, baseband unit and radio were all located inan equipment enclosure at the bottom of the tower to provide easy accessfor maintenance, repair and/or later upgrades to the equipment. Coaxialcable(s) were routed from the equipment enclosure to the top of thetower that carried signal transmissions between the radio and theantennas.

FIG. 1 schematically illustrates a conventional cellular base station10. As shown in FIG. 1, the cellular base station 10 includes anequipment enclosure 20 and a tower 30. The equipment enclosure 20 istypically located at the base of the tower 30, as shown in FIG. 1. Abaseband unit 22, a radio 24 and a power supply 26 are located withinthe equipment enclosure 20. The baseband unit 22 may be in communicationwith a backhaul communications system 44. A plurality of antennas 32(e.g., three sectorized antennas 32-1, 32-2, 32-3) are located at thetop of the tower 30. Three coaxial cables 34 (which are bundled togetherin FIG. 1 to appear as a single cable) connect the radio 24 to theantennas 32. The antennas 32 are passive (unpowered) devices and hencenone of the equipment at the top of the tower 30 require electricalpower. Note that herein when multiple units of an element are provided,each individual unit may be referred to individually by the referencenumeral for the element followed by a dash and the number for theindividual unit (e.g., antenna 32-2), while multiple units of theelement may be referred to collectively by their base reference numeral(e.g., the antennas 32).

In recent years, a shift has occurred and the radio 24 is now moretypically located at the top of the tower 30 in new or upgraded cellularinstallations. Radios that are located at the top of the tower 30 aretypically referred to as remote radio heads (“RRH”) 24′. Using RRHs 24′may significantly improve the quality of the cellular data signals thatare transmitted and received by the cellular base station as the use ofRRHs 24′ may reduce signal transmission losses and noise. In particular,as the coaxial cable runs up the tower may be 100-200 feet or more, thesignal loss that occurs in transmitting signals at cellular frequencies(e.g., 1.8 GHz, 3.0 GHz, etc.) over the coaxial cable may besignificant. Because of this loss in signal power, the signal-to-noiseratio of the RF signals may be degraded in systems that locate the radio24 at the bottom of the tower 30 as compared to cellular base stationswhere RRHs 24′ are located at the top of the tower 30 next to theantennas 32 (note that signal losses in the cabling connection betweenthe baseband unit 22 at the bottom of the tower 30 and the RRH 24′ atthe top of the tower 30 may be much smaller, as these signals aretransmitted at baseband frequencies as opposed to RF frequencies).

FIG. 2 is a schematic diagram that illustrates a cellular base station10′ according to this newer architecture. As shown in FIG. 2, thebaseband unit 22 and the power supply 26 may still be located at thebottom of the tower 30 in the equipment enclosure 20. The radio 24 inthe form of an RRH 24′ is located at the top of the tower 30 immediatelyadjacent to the antennas 32. While the use of tower-mounted RRHs 24′ mayimprove signal quality, it also, unfortunately, requires that DC powerbe delivered to the top of the tower 30 to power the RRH 24′. In somecases, the DC power may be delivered over a coaxial cable (not shown)that also carries communications between the baseband unit 22 and theRRH 24′. As shown in FIG. 2, more typically a fiber optic cable 38connects the baseband unit 22 to the RRH 24′ (as fiber optic links mayprovide greater bandwidth and lower loss transmissions), and a separatepower cable 36 is provided for delivering the DC power signal to the RRH24′. The separate power cable 36 is typically bundled with the fiberoptic cable 38 so that they may be routed up the tower 30 together.

SUMMARY

Pursuant to embodiments of the present invention, methods of powering aradio that is mounted on a tower of a cellular base station (or otherlocation remote from an associated baseband unit) are provided in whicha DC power signal is output from a power supply and the DC power signalthat is output from the power supply is supplied to the radio over apower cable. A voltage level of the DC power signal that is output fromthe power supply is adjusted so that the DC power signal at a radio endof the power cable that is remote from the power supply has asubstantially constant voltage notwithstanding variation in a currentlevel of the DC power signal.

In some embodiments, the power supply may be a programmable powersupply, and the method may further include inputting information to thepower supply from which the voltage level of the DC power signal that isoutput from the power supply can be computed that will provide the DCpower signal at the radio end of the power cable that has thesubstantially constant voltage. In such embodiments, the informationthat is input to the power supply may be a resistance of the powercable, or may be a length of the power cable and a diameter of theconductive core of the power cable.

In some embodiments, a current level of the DC power signal that isoutput from the power supply may be measured, and the voltage level ofthe DC power signal that is output by the power supply may beautomatically adjusted in response to changes in the measured outputcurrent of the DC power signal that is output from the power supply toprovide the DC power signal at the radio end of the power cable that hasthe substantially constant voltage.

In some embodiments, the programmable power supply may be a DC-to-DCconverter that receives a DC power signal that is output from a secondpower supply and adjusts a voltage level of the DC power signal that isoutput from the second power supply to provide the DC power signal atthe radio end of the power cable that has the substantially constantvoltage. The substantially constant voltage may be a voltage thatexceeds a nominal power signal voltage of the radio and which is lessthan a maximum power signal voltage of the radio.

In some embodiments, a signal may be transmitted over the power cablethat is used to determine an electrical resistance of the power cable.In some embodiments, the substantially constant voltage may besignificantly higher than a maximum power signal voltage of the radio,and a tower-mounted DC-to-DC converter may be used to reduce a voltageof the power signal at the radio end of the power cable to a voltagethat is less than the maximum power supply voltage of the radio.

Pursuant to further embodiments of the present invention, cellular basestation systems are provided that include a tower with at least oneantenna mounted thereon, an RRH mounted on the tower, a baseband unitthat is in communication with the RRH, a programmable power supplylocated remotely from the RRH; and a power cable having a first end thatreceives a DC power signal from the programmable power supply and asecond end that provides the DC power signal to the RRH. Theprogrammable power supply is configured to provide a substantiallyconstant voltage at the second end of the power cable by adjusting avoltage level of the DC power signal output by the programmable powersupply based on the current level output by the programmable powersupply and a resistance of the power cable.

In some embodiments, the programmable power supply may include a userinterface that is configured to receive a resistance of the power cableand/or information regarding characteristics of the power cable fromwhich the resistance of the power cable may be calculated. Theprogrammable power supply may further include a current measurementmodule that measures a current output by the power supply. Theprogrammable power supply may also include a feedback loop that adjuststhe voltage level of the DC power signal output of the power supplybased on the measured current output by the power supply.

Pursuant to still further embodiments of the present invention,programmable power supplies are provided that include an input; aconversion circuit that is configured to convert an input signal into aDC output signal that is output through an output port; a current sensorthat senses an amount of current output through the output port; a userinput that is configured to receive information relating to theresistance of a cabling connection between the programmable power supplyoutput port and a radio; and a control module that is configured tocontrol the conversion circuit in response to information relating tothe resistance of the cabling connection and the sensed amount ofcurrent to adjust the voltage of the output signal that is outputthrough the output port so that the voltage at the far end of thecabling connection may remain substantially constant despite changes inthe current drawn by the radio.

In some embodiments, the information relating to the resistance of thecabling connection may comprise a length of the cabling connection and asize of the conductor of the cabling connection.

Pursuant to additional embodiments of the present invention, methods ofpowering a cellular radio that is located remotely from a power supplyand an associated baseband unit and that is connected to the powersupply by a cabling connection are provided in which a DC power signalis output from the power supply and the DC power signal that is outputfrom the power supply is supplied to the radio over the cablingconnection. A voltage level of the DC power signal that is output fromthe power supply is adjusted in response to a current level of the DCpower signal that is output from the power supply so that the voltage ofthe DC power signal at a radio end of the cabling connection ismaintained at a pre-selected level, range or pattern.

In some embodiments, the voltage level of the DC power signal that isoutput from the power supply is adjusted in response to a feedbacksignal that is transmitted to the power supply from a remote location.The feedback signal may include information regarding the measuredvoltage of the DC power signal at the radio end of the power cable.

Pursuant to yet additional embodiments of the present invention, methodsof powering a radio that is mounted on a tower of a cellular basestation (or other location remote from an associated baseband unit) areprovided in which a DC power signal is output from a power supply andthe DC power signal that is output from the power supply is supplied tothe radio over a power cable. A voltage of the DC power signal ismeasured at a radio end of the power cable that is remote from the powersupply. Information regarding the measured voltage of the DC powersignal at the radio end of the power cable is communicated to the powersupply. A voltage level of the DC power signal that is output from thepower supply is adjusted in response to the received informationregarding the measured voltage of the DC power signal at the radio endof the power cable.

In some embodiments, the voltage level of the DC power signal that isoutput from the power supply may be adjusted in response to the receivedinformation to maintain the DC power signal at the radio end of thepower cable at a substantially constant voltage notwithstandingvariation in a current level of the DC power signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified, schematic view of a traditional cellular basestation architecture.

FIG. 2 is a simplified, schematic view of a conventional cellular basestation in which a remote radio head is located at the top of theantenna tower.

FIG. 3 is a simplified, schematic view of a cellular base stationaccording to embodiments of the present invention.

FIG. 4 is a schematic block diagram of a programmable power supplyaccording to embodiments of the present invention.

FIG. 5 is a schematic block diagram of a programmable power supplyaccording to further embodiments of the present invention.

FIG. 6 is a simplified, schematic view of a cellular base stationaccording to still further embodiments of the present invention.

FIG. 7 is a simplified, schematic view of a cellular base stationaccording to yet additional embodiments of the present invention.

FIG. 8 is a simplified, schematic view of a cellular base stationaccording to yet further embodiments of the present invention.

FIG. 9 is a flow chart illustrating operations of methods according toembodiments of the present invention.

DETAILED DESCRIPTION

Pursuant to embodiments of the present invention, methods for deliveringDC power to a remote radio head (“RRH”) of a cellular base station areprovided, along with related cellular base stations and programmablepower supplies. These methods, systems and power supplies may allow forlower power supply currents, which may reduce the power loss associatedwith delivering the DC power signal from the power supply at the base ofa tower of the cellular base station to the RRH at the top of the tower.Since cellular towers may be hundreds of feet tall and the voltage andcurrents required to power the RRH may be quite high (e.g., about 50Volts at about 20 Amperes of current), the power loss that may occuralong the hundreds of feet of cabling may be significant. Thus, themethods according to embodiments of the present invention may providesignificant power savings which may reduce the costs of operating acellular base station.

The DC voltage of a power signal that is supplied to an RRH from a powersupply over a power cable may be determined as follows:V _(RRH) =V _(PS) −V _(Drop)  (1)where V_(RRH) is the DC voltage of the power signal delivered to theRRH, V_(PS) is the DC voltage of the power signal that is output by thepower supply, and V_(Drop) is the decrease in the DC voltage that occursas the DC power signal traverses the power cable connecting the powersupply to the RRH. V_(Drop) may be determined according to Ohm's Law asfollows:V _(Drop) =I _(RRH) *R _(Cable)  (2)where R_(Cable) is the cumulative electrical resistance (in Ohms) of thepower cable connecting the power supply to the RRH and I_(RRH) is theaverage current (in Amperes) flowing through the power cable to the RRH.

The electrical resistance R_(cable) of the power cable is inverselyproportional to the diameter of the conductor of the power cable(assuming a conductor having a circular cross-section). Thus, the largerthe diameter of the conductor (i.e., the lower the gauge of theconductor), the lower the resistance of the power cable. Typically,power cables utilize copper conductors due to the low resistance ofcopper. Copper resistance is specified in terms of unit length,typically milliohms (mΩ)/ft; as such, the cumulative electricalresistance of the power cable increases with the length of the cable.Thus, the longer the power cable, the higher the voltage drop V_(Drop).

Typically, a minimum required voltage for the power signal, a nominal orrecommended voltage for the power signal and a maximum voltage for thepower signal will be specified for the RRH. Thus, the power supply atthe base of the tower must output a voltage V_(PS) such that V_(RRH)will be between the minimum and maximum specified voltages for the powersignal of the RRH. As V_(Drop) is a function of the current I_(RRH) thatis supplied to the RRH (see Equation 2 above), if V_(PS) (the voltageoutput by the power supply) is constant, then the voltage V_(RRH) of thepower signal that is delivered to the RRH will change with the variationin current drawn by the RRH. Conventionally, the voltage output by thepower supply (V_(PS)) is set to ensure that a power signal having thenominal voltage is supplied to the RRH (or at least a value above theminimum required voltage for the power signal) when the RRH draws themaximum anticipated amount of current.

The power that is lost (P_(Loss)) in delivering the power signal to theRRH over a power cable may be calculated as follows:P _(Loss) =V _(Cable) *I _(RRH)=(I _(RRH) *R _(Cable))*I _(RRH) =I_(RRH) ² *R _(Cable)  (3)where V_(Cable)=the average voltage drop in Volts along the power cable.In order to reduce or minimize P_(Loss), the power supply may be set tooutput a DC power signal that, when it arrives at the RRH, will have themaximum voltage specified for the RRH, as the higher the voltage of thepower signal that is delivered to the RRH the lower the current I_(RRH)of the power signal on the power cable. As is apparent from Equation 3above, the lower the current I_(RRH) of the power signal on the powercable, the lower the power loss P_(Loss).

Pursuant to embodiments of the present invention, the power supply maycomprise a programmable power supply which may (1) sense the currentbeing drawn by the RRH (or another equivalent parameter) and (2) adjustthe voltage of the power signal that is output by the power supply tosubstantially maintain the voltage of the power signal that is suppliedto the RRH at or near a desired value, which may be, for example, themaximum voltage for the power signal that may be input to the RRH. Inorder to accomplish this, the resistance of the power cable may be inputto the programmable power supply or, alternatively, other informationsuch as, for example, the length and size of the power cable, or theimpedance of the power cable, may be input to the programmable powersupply and the programmable power supply may determine the resistance ofthe power cable from this information. As the current drawn by the RRHvaries, the programmable power supply may adjust the voltage of itsoutput power signal to a voltage level that will deliver a power signalhaving a preselected voltage (e.g., the maximum supply voltage of theRRH minus a buffer) to the RRH. As shown by Equation 3 above, this willreduce or minimize the power loss along the power cable, and hence mayreduce the cost of powering the RRH. As a typical RRH may require abouta kilowatt of power and may run 24 hours a day, seven days a week, andas a large number of RRHs may be provided at each cellular base station(e.g., three to twelve), the power savings may be significant.

Embodiments of the present invention will now be discussed in moredetail with reference to FIGS. 3-7, in which example embodiments of thepresent invention are shown.

FIG. 3 is a schematic block diagram of a cellular base station 100according to embodiments of the present invention. As shown in FIG. 3,the cellular base station 100 includes an equipment enclosure 20 and atower 30. The tower 30 may be a conventional antenna or cellular toweror may be another structure such as a utility pole or the like. Abaseband unit 22, a first power supply 26 and a second power supply 28are located within the equipment enclosure 20. An RRH 24′ and pluralityof antennas 32 (e.g., three sectorized antennas 32-1, 32-2, 32-3) aremounted on the tower 30, typically near the top thereof.

The RRH 24′ receives digital information and control signals from thebaseband unit 22 over a fiber optic cable 38 that is routed from theenclosure 20 to the top of the tower 30. The RRH 24′ modulates thisinformation into a radio frequency (“RF”) signal at the appropriatecellular frequency that is then transmitted through one or more of theantennas 32. The RRH 24′ also receives RF signals from one or more ofthe antennas 32, demodulates these signals, and supplies the demodulatedsignals to the baseband unit 22 over the fiber optic cable 38. Thebaseband unit 22 processes the demodulated signals received from the RRH24′ and forwards the processed signals to the backhaul communicationssystem 44. The baseband unit 22 also processes signals received from thebackhaul communications system 44 and supplies them to the RRH 24′.Typically, the baseband unit 22 and the RRHs 24 each includeoptical-to-electrical and electrical-to-optical converters that couplethe digital information and control signals to and from the fiber opticcable 38.

The first power supply 26 generates one or more direct current (“DC”)power signals. The second power supply 28 in the embodiment of FIG. 3comprises a DC-to-DC converter that accepts the DC power signal outputby the first power supply 26 as an input and outputs a DC power signalhaving a different voltage. A power cable 36 is connected to the outputof the second power supply 28 and is bundled together with the fiberoptic cable 3$ so that the two cables 36, 38 may be routed up the tower30 as an integral unit. While the first power supply 26 and the secondpower supply 28 are illustrated as separate power supply units in theembodiment of FIG. 3, it will be appreciated that the two power supplies26, 28 may be combined into a single power supply unit in otherembodiments.

As noted above, pursuant to embodiments of the present invention, DCpower supplies are provided that may deliver a power signal to a remoteRRH with reduced power loss. In the embodiment of FIG. 3, the powersupply 28 comprises a programmable power supply that receives an inputDC power signal from power supply 26 and outputs a DC power signal tothe power cable 36. The voltage of the DC power signal output by thepower supply 28 may vary in response to variations in the current of theDC power signal drawn from the power supply 28 by the RRH 24′. Inparticular, the voltage of the DC power signal output by the powersupply 28 may be set so that the voltage of the DC power signal at thefar end of the power cable 36 (i.e., the end adjacent the RRH 24′) isrelatively constant. If the voltage of the DC power signal at the farend of power cable 36 is set to be approximately the maximum specifiedvoltage for the power signal of the RRH 24′, then the power lossassociated with supplying the DC power signal to the RRH 24′ over thepower cable 36 may be reduced, since the higher DC power signal voltagewill correspondingly reduce the current of the DC power signal that issupplied over the power cable 36.

State-of-the-art RRHs are most typically designed to be powered by a 48Volt (nominal) DC power signal. While the minimum DC power signalvoltage at which the RRH 24′ will operate and the maximum DC powersignal voltage that may be provided safely to the RRH 24′ without thethreat of damage to the RRH 24′ vary, typical values are a 38 Voltminimum DC power signal voltage and a 56 Volt maximum DC power signalvoltage. Thus, according to embodiments of the present invention, theprogrammable power supply 28 may be designed to deliver a DC powersignal having a relatively constant voltage of, for example, about 54 or52 Volts at the far end of the power cable 36 (i.e., about, 2-4 Voltsless than the maximum DC power signal voltage for the RRH 24′) in orderto reduce the power loss associated with the voltage drop that the DCpower signal experiences traversing the power cable 36.

In order to maintain the voltage of the DC power signal at the far endof the power cable 36 at or near a predetermined value it may benecessary to know two things. First, the current of the DC power signaldrawn from the power supply must be known, as Equations 1 and 2 showthat V is a function of I_(RRH). Second, the resistance R_(cable) of thepower cable 36 must also be known, as it too affects the voltage drop.The programmable power supplies according to embodiments of the presentinvention may be configured to measure, estimate, calculate or receiveboth values.

For example, FIG. 4 is a block diagram of a programmable power supply150 in the form of a DC-to-DC converter according to certain embodimentsof the present invention that may be used as the power supply 28 of FIG.3. As shown in FIG. 4, the programmable power supply 150 includes aninput 152, a conversion circuit 154 and an output 156. The power supply150 further includes a current sensor 158, a user input 160, controllogic 162 and a memory 164.

The input 152 may receive a DC power signal such as the DC power signaloutput by power supply 26 of FIG. 3. The DC power signal that isreceived at input 152 may be a DC power signal having a relativelyconstant voltage in some embodiments. The conversion circuit 154 may bea circuit that is configured to convert the voltage of the signalreceived at input 152 to a different DC voltage. A wide variety of DCconversion circuits are known in the art, including, for example,electronic, electrochemical and electromechanical conversion circuits.Most typically electronic circuits using inductors or transformers areused to provide high efficiency voltage conversion. The output 156 mayoutput the DC power signal having the converted voltage.

The current sensor 158 may be any appropriate circuit that senses thecurrent level of the DC power signal output through the output 156. Thecurrent drawn by the RRH 24′ may vary over time depending upon, forexample, the number of carriers that are transmitting at any given timeand whether the RRH is in a steady-state mode, powering up or rebooting.The current sensor 158 may sense the current level of the DC powersignal at output 156 and provide the sensed current level to the controllogic 162. The control logic 162 may then adjust parameters of theconversion circuit 154 so as to adjust the voltage of the DC powersignal output through output 156 so that the voltage at the far end ofthe power cable 36 that is attached to output 156 may remainsubstantially constant despite changes in the current drawn by the RRH24′ and corresponding changes in the voltage drop that occurs over thepower cable 36.

While FIG. 4 illustrates a power supply 150 that comprises a DC-to-DCconverter, it will be appreciated that in other embodiments an AC-to-DCconverter may be used instead. In such embodiments, the input 152receives an alternating current (“AC”) power signal and the conversioncircuit 154 converts the AC power signal to a DC power signal and alsoadjusts the voltage level of the DC power signal that is output throughoutput 156 to an appropriate level in the manner discussed above.

As noted above, in some embodiments, the voltage of the power signalthat is output by the power supply 150 may be set so that the voltage atthe far end of the power cable 36 remains at or near a predeterminedvoltage level that is just under a maximum power signal voltage levelthat the RRH 24′ may handle. In order to achieve this, it is necessaryto know the voltage drop that the DC power signal will experiencetraversing the power cable 36, as this voltage drop affects the voltageof the DC power signal at the far end of the power cable 36. In someembodiments, the user input 160 to the power supply 150 allows a user toinput a cumulative resistance value for the power cable 36 which theuser may obtain by, for example, calculation (based on the length, sizeand material of the conductor of the power cable 36), measurement (done,for example, by transmitting a signal over the power cable 36 andmeasuring the voltage of the signal output at the far end of the powercable 36) or a combination thereof (e.g., measuring or estimating acumulative impedance value for the power cable 36 and converting thiscumulative impedance value into a cumulative resistance value). In otherembodiments, the user may input physical characteristics of the powercable 36 such as size, length, conductor material, model number, etc.)and algorithms, equations, look-up tables and the like that are storedin the memory 164 of the power supply 150 may be used to calculate orestimate the resistance of the power cable 36.

In some embodiments, the second power supply 28 of FIG. 3 may further beconfigured to measure a resistance of the power cable 36. For example,FIG. 5 is a block diagram of a programmable power supply 150′ accordingto further embodiments of the present invention that may be used toimplement the power supply 28 of FIG. 3. The power supply 150′ is verysimilar to the power supply 150 of FIG. 4, except that it furtherincludes a cable resistance measurement circuit 170 that may be used tomeasure a resistance of the power supply cable. The cable resistancemeasurement circuit 170 may be implemented in a variety of ways. Forexample, in some embodiments, the cable resistance measurement circuit170 may transmit a voltage pulse onto the power cable and measure thereflected return pulse (the far end of the power cable may be terminatedwith a termination having known characteristics). The current of thevoltage pulse may be measured, as well as the voltage level of thereflected return pulse. The control logic 162 may then apply Ohm's lawto calculate the resistance of the power cable. In other embodiments, atthe far end of the power cable the two conductors thereof may be shortedand a voltage pulse may again be transmitted through the power cable.The current level of the pulse and the voltage level of the return pulsemay be measured and the control logic 162 may again use these measuredvalues to calculate the resistance of the power cable. In otherembodiments, the DC resistance can be measured by transmittingalternating current signals at different frequencies over the powercable and measuring the amplitude and phase shift of these signals atthe far end of the cable. The DC resistance may then be calculated usingthe measured results. Other ways of measuring the resistance of a wiresegment are known to those of skill in the art and may be used insteadof the example methods listed above.

It will also be appreciated that in other embodiments the resistancemeasurement circuit 170 may measure an impedance of the power cable anduse this measured impedance value to determine the resistance of thepower cable. It will also be appreciated that the power supply 150′ mayalternatively comprise an AC-to-DC converter, similar to power supply150 discussed above.

Another technique for reducing the power loss associated with supplyingpower to a tower-mounted RRH of a cellular base station is todramatically increase the voltage of the DC power signal fed to thepower cable that supplies the DC power signal to the RRH (i.e., wellbeyond the maximum voltage for the DC power signal that can be handledby the RRH), and then using a tower-mounted DC-to-DC converter powersupply to step-down the voltage of the DC power signal to a voltagelevel that is appropriate for the RRH. As the increased voltage reducesthe current necessary to supply the wattage required by the RRH, thepower loss along the power cable may be reduced (see Equation 2 above).This is referred to as a “Buck-Boost” scheme where the first DC-to-DCconverter at the bottom of the tower is a “Boost” converter thatincreases the voltage of the DC power signal above the necessary levelto operate the RRH and the second DC-to-DC converter at the top of thetower is a “Buck” converter that reduces the voltage of the DC powersignal to a desired level. FIG. 6 is a simplified, schematic view of acellular base station 200 that implements such a technique.

As shown in FIG. 6, the cellular base station 200 is similar to thecellular base station 100 described above with reference to FIG. 3,except that the cellular base station 200 further includes a third powersupply 42 in the form of a tower-mounted DC-to-DC converter. In thedepicted embodiment, the second power supply 28 of FIG. 3 is omitted,and the first power supply 26 is configured to supply a DC power signalhaving a voltage that is significantly higher than the maximum voltagefor the DC power signal that may be supplied to the RRH 24′ (e.g., a 150volt DC power signal). This high voltage DC power signal may experiencesignificantly less power loss when traversing the power cable 36. TheDC-to-DC converter 42 is mounted at the top of the tower 30 between thefar end of cable 36 and the RRH 24′. The DC-to-DC converter 42 may be aBuck converter that decreases the voltage of the DC power signalreceived over the power cable 36 to a voltage level appropriate forsupply to the RRH 24′.

As is shown in FIG. 7, in other embodiments, the second power supply 28may be included in the form of, for example, a DC-to-DC Boost powerconverter 28 that supplies a high voltage DC power signal (e.g., 150volts) to the power cable 36. In this embodiment, a DC-to-DC converteris provided at both ends of the power cable 36 so that both of theabove-described techniques for reducing power losses in the power cable36 may be implemented. In particular, the second power supply 28 mayoutput a DC power signal having high voltage (e.g., on the order of 150volts) that fluctuates with power requirements of the load so that theDC power signal that is supplied at the far end of power cable 36 is setat a relatively constant value. The tower-mounted DC-to-DC converter 42may be a simple device that down-converts the voltage of the DC powersignal by a fixed amount X. The power supply 28 may be programmed todeliver a DC power signal to the tower-mounted DC-to-DC converter 42that has a voltage level that is set as follows:Voltage of Delivered Power Signal=V _(RRH-Max) −V _(margin) +X  (4)where V_(RRH-Max) is the maximum power signal voltage that the RRH 24′is specified to handle, V_(margin) is a predetermined margin (e.g., 2Volts), and X is the magnitude of the voltage conversion applied by thetower-mounted DC-to-DC converter 42.

One disadvantage of the approaches of FIGS. 6 and 7 is that they requirethe installation of additional equipment (i.e., the DC-to-DC converter42) at the top of the tower 30. As the cost associated with sending atechnician up a tower may be very high, there is generally a preferenceto reduce or minimize, where possible, the amount of equipment that isinstalled at the top of a cellular base station tower, and the equipmentthat is installed at the top of cellular towers tends to be expensive asit typically is designed to have very low failure rates and maintenancerequirements in order to reduce the need for technician trips up thetower to service the equipment. The inclusion of an additional DC-to-DCconverter 42 also represents a further increase in capital expenditures,which must be weighed against the anticipated savings in operatingcosts.

Thus, pursuant to embodiments of the present invention, a DC powersignal may be supplied to a tower-mounted RRH (or other equipment) of acellular base station over a power cable, where the DC power signal thatis supplied to the RRH may have a relatively constant voltage level,regardless of the current drawn by the RRH. The voltage level of the DCpower signal supplied to the RRH may be set to be at or near a maximumpower signal voltage that the RRH can handle, thereby reducing the powerloss of the DC power signal. In this manner, the operating costs for thecellular base station may be reduced.

In some embodiments, the programmable power supply according toembodiments of the present invention may comprise a DC-to-DC converterthat may be connected between a power supply of an existing base stationand the power cable that supplies the power signal to a tower-mountedRRH. Thus, by adding a single piece of equipment at the bottom of thetower, an existing cellular base station may be retrofitted to obtainthe power savings available using the techniques according toembodiments of the present invention.

While the above-described embodiments of cellular base stationsaccording to embodiments of the present invention include a first,conventional DC power supply 26 and a second DC-to-DC converter powersupply 28, it will be appreciated that in other embodiments these twopower supplies may be replaced with a single programmable power supplythat may be configured to output a relatively constant voltage at thefar end of the power cable 36 in the manner described above.

Pursuant to further embodiments of the present invention, a feedbackloop may be used to control the voltage of the DC power signal output bythe DC power supply so that the voltage of the DC power signal at thefar end of the power cable that connects the power supply and the RRH ismaintained at a desired level. FIG. 8 is a simplified, schematic view ofone example embodiment of a cellular base station 400 that implementssuch a technique.

As shown in FIG. 8, the cellular base station 400 is similar to thecellular base station 100 described above with reference to FIG. 3,except that the cellular base station 400 further includes a DC powersignal voltage control module 50 that is co-located with the RRH 24′.The DC power signal voltage control module 50 may be located, forexample, at or near the top of the tower 30. In an example embodiment,the DC power signal voltage control module 50 may include a voltagemeter 52, a controller 54 and a communications module 56. The voltagemeter 52 may be used to monitor the voltage of the DC power signal atthe far end of the power cable 36 (i.e., at the top of the tower 30).Any appropriate voltage meter may be used that is capable of measuringthe voltage of the DC power signal at the far end off cable 36 (or atanother location proximate the RRH 24′) or that may measure otherparameters which may be used to determine the voltage of the DC powersignal at the far end off cable 36.

The voltage meter 52 may supply the measured voltage (or otherparameter) to the controller 54. The controller 54 may then control thecommunications module 56 to transmit the measured or calculated voltageof the DC power signal at the far end of power cable 36 to, for example,the second power supply 28. The controller 54 may comprise anyappropriate processor, controller, ASIC, logic circuit or the like. Thecommunications module 56 may comprise a wired or wireless transmitter.In some embodiments, the communications module 56 may comprise awireless Bluetooth transmitter or a cellular transmitter. In otherembodiments, the communications module 56 may communicate with thesecond power supply 28 over a separate wired connection. In still otherembodiments, the communications module 56 may communicate with thesecond power supply 28 by modulating a signal onto the power cable 36.In each case, the communications module 56 may transmit the measured orcalculated voltage of the DC power signal at the far end of power cable36 to the second power supply 28. The second power supply 28 may adjustthe voltage of the DC power signal that it outputs in response to thesecommunications in order to generally maintain the voltage of the DCpower signal at the far end of power cable 36 at a desired and/orpre-selected level. Thus, in this embodiment, an active feedback loopmay be used to maintain the voltage of the DC power signal at the farend of power cable 36 at the pre-selected level.

The power signal voltage control module 50 may be a standalone unit ormay be integrated with other equipment such as, for example, the RRH24′.

While the embodiments that have been described above deliver a DC powersignal over the power cable 36, it will be appreciated that in otherembodiments, an AC power signal may be used instead. For example, if theRRHs 24′ are designed to be powered by an AC power signal as opposed toa DC power signal, then the power supply 28 may output an AC powersignal as opposed to a DC power signal, but may otherwise operate in thesame fashion. Likewise, in embodiments that include a DC-to-DC converter42 at the top of the tower 30, an AC-to-DC converter may be used insteador, if the RRH 24′ is designed to be powered by an AC power signal, theDC-to-DC converter 42 may be replaced with a Buck AC-to-AC converter.Thus, it will be appreciated that the embodiments illustrated in thefigures are exemplary in nature and are not intended to limit the scopeof the present invention.

In the various embodiments described above, a single power cable 36 hasbeen provided that connects the power supply 28 to the RRH 24′. It willbe appreciated, however, that the cabling connection for the powersignal between the power supply 28 and the RRH 24′ may include multipleelements such as two or more power cables 36 that are connected byconnectors in other embodiments.

A method of powering a radio that is mounted on a tower of a cellularbase station according to embodiments of the present invention will nowbe described with reference to the flow chart of FIG. 9. As shown inFIG. 9, operations may begin with a user inputting information to aprogrammable power supply which may be used by the programmable powersupply to set a voltage level of the power signal that is output by theprogrammable power supply (block 300). This information may comprise,for example, an electrical resistance of a cabling connection betweenthe power supply and the radio or information regarding thecharacteristics of the cabling connection that may be used to calculatethis resistance. While not shown in FIG. 9, it will be appreciated thatin other embodiments the programmable power supply may have thecapability to measure the resistance of the cabling connection, therebyavoiding the need for any user input. The programmable power supply mayuse this information to output a DC power signal that is provided to theradio over the cabling connection (block 310). The current of the DCpower signal that is output may then be measured (block 320). Theprogrammable power supply may then automatically adjust a voltage levelof the power signal output by the power supply in response to changes inthe measured output current so as to provide a substantially constant,preselected voltage at a first end of the power cable that is remotefrom the power supply (block 330). As shown in FIG. 9, blocks 320 and330 are then performed continuously at appropriate intervals in order tomaintain the voltage level of the signal output of the power supply atthe far end of the power cable at the preselected voltage level.

Embodiments of the present invention provide power supplies for poweringradio equipment such as a remote radio head that is located remote fromthe power supply used to power the radio (e.g., the power supply is atthe base of a cellular tower and the radio is at the top of the tower)without receiving any feedback from the radio or from other equipment atthe remote location. The voltage of the DC power signal supplied by thepower supply to the radio over a cabling connection may be set at apre-selected level. The pre-selected level may be set to reduce orminimize power losses that may be incurred in transmitting the DC powersignal over the cabling connection. The voltage of the DC power signaloutput by the power supply may be varied based on variations in thecurrent drawn from the power supply so that the voltage of the DC powersignal at the radio end of the cabling connection may have, for example,a substantially constant value. This value may be selected to be near amaximum value for the voltage of the DC power signal that may be inputto the radio.

While typically the voltage of the DC power signal output by the powersupply will be adjusted to maintain the voltage of the DC power signalat the radio end of the cabling connection at a set level, it will beappreciated that some variation is to be expected because of the time ittakes the DC power supply to adjust the voltage of the DC power signalin response to changes in the current drawn. It will also be appreciatedthat the voltage of the DC power signal need not be maintained at aconstant level at the radio end of the cabling connection but, mayinstead have different characteristics (e.g., set to be maintainedwithin a predetermined range, set to return to a pre-selected levelwithin a certain time period, etc.) in some embodiments.

In some current cellular systems, the voltage drop that occurs on the DCpower signal that is delivered from a power supply located at the bottomof a cellular tower to the RRH at the top of the tower may be so largethat the voltage of the DC power signal at the top of the tower may beinsufficient to run the RRH. As a result, larger diameter power cablesare used in some cases that exhibit less DC resistance and hence asmaller voltage drop. However, the use of larger power cables has anumber of disadvantages, as these cables can be significantly moreexpensive, add more weight to the tower (requiring that the towers beconstructed to handle this additional weight) and more difficult toinstall.

Pursuant to embodiments of the present invention, this problem may bereduced or solved by controlling the voltage of the DC power signaloutput by the power supply so that the voltage of the DC power signal atthe radio end of the cabling connection may be at or near a maximumvoltage for the DC power signal that may be input to the RRH. Thisscheme reduces the voltage drop of the DC power signal, and hence mayallow for the use of smaller diameter power cables and/or longer cablingconnections between the power supply and the RRH. Additionally, as notedabove, as the power losses experienced by the DC power signal are less,the costs of operating the RRH may also be reduced.

The present invention has been described with reference to theaccompanying drawings, in which certain embodiments of the invention areshown. This invention may, however, be embodied in many different formsand should not be construed as limited to the embodiments that arepictured and described herein; rather, these embodiments are provided SQthat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout the specification anddrawings. It will also be appreciated that the embodiments disclosedabove can be combined in any way and/or combination to provide manyadditional embodiments.

It will be understood that, although the terms first, second, etc. areused herein to describe various elements, these elements should not belimited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

Unless otherwise defined, all technical and scientific terms that areused in this disclosure have the same meaning as commonly understood byone of ordinary skill in the art to which this invention belongs. Theterminology used in the above description is for the purpose ofdescribing particular embodiments only and is not intended to belimiting of the invention. As used in this disclosure, the singularforms “a”, “an” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise. It will also beunderstood that when an element (e.g., a device, circuit, etc.) isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

It will be further understood that the terms “comprises” “comprising,”“includes” and/or “including” when used herein, specify the presence ofstated features, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,operations, elements, components, and/or groups thereof.

In the drawings and specification, there have been disclosed typicalembodiments of the invention and, although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation, the scope of the invention being set forth inthe following claims.

That which is claimed is:
 1. A method of powering a cellular radio thatis remote from an associated baseband unit, the method comprising:outputting a direct current (“DC”) power signal from a power supply andsupplying the DC power signal that is output from the power supply tothe cellular radio over a power cable; and adjusting a voltage level ofthe DC power signal that is output from the power supply so that the DCpower signal at a radio end of the power cable that is remote from thepower supply has a substantially constant voltage notwithstandingvariation in a current level of the DC power signal that is output fromthe power supply, wherein the substantially constant voltage of the DCpower signal at the radio end of the power cable exceeds a nominal powersignal voltage of the cellular radio and is within 4 volts of a maximumpower signal voltage of the cellular radio so as to reduce power loss inthe power cable as compared to the power loss that occurs in the powercable when the DC power signal at the radio end of the power cable is atthe nominal power signal voltage.
 2. The method of claim 1, the methodfurther comprising measuring the current level of the DC power signalthat is output from the power supply, wherein the voltage level of theDC power signal that is output by the power supply is automaticallyadjusted in response to changes in the measured current level of the DCpower signal that is output from the power supply to provide the DCpower signal at the radio end of the power cable that has thesubstantially constant voltage.
 3. The method of claim 2, wherein thepower supply comprises a DC-to-DC converter that receives a DC powersignal from a second power supply and adjusts a voltage level of the DCpower signal that is received from the second power supply to providethe DC power signal at the radio end of the power cable that has thesubstantially constant voltage.
 4. The method of claim 2, furthercomprising transmitting a control signal over the power cable that isused to determine an electrical resistance of the power cable.
 5. Themethod of claim 2, wherein the substantially constant voltage is atleast 4 Volts above the nominal power signal voltage of the cellularradio and less than the maximum power signal voltage of the cellularradio.
 6. The method of claim 2, further comprising: transmitting asignal over the power cable; measuring a level of a signal received inresponse to the transmitted signal; and using the measured level of thereceived signal to determine an amount to adjust the voltage level ofthe DC power signal.
 7. The method of claim 6, wherein the signalreceived in response to the transmitted signal is a reflection of thetransmitted signal.
 8. A method of powering a cellular radio that islocated remotely from a power supply and that is connected to the powersupply by a cabling connection, the method comprising: outputting adirect current (“DC”) power signal from the power supply and supplyingthe DC power signal that is output from the power supply to the cellularradio over the cabling connection; and adjusting a voltage level of theDC power signal that is output from the power supply in response to acurrent level of the DC power signal that is output from the powersupply so that a voltage of the DC power signal at a radio end of thecabling connection is maintained at a level that exceeds a nominal DCpower supply voltage for the cellular radio by at least 4 Volts and thatis less than a maximum power signal voltage of the cellular radio. 9.The method of claim 8, wherein the voltage level of the DC power signalthat is output from the power supply is adjusted in response to afeedback signal that is transmitted to the power supply from a remotelocation.
 10. The method of claim 9, wherein the feedback signalincludes information regarding a measured voltage of the DC power signalat the radio end of the cabling connection.
 11. A method of powering aradio that is mounted on a tower of a cellular base station, or otherlocation remote from an associated baseband unit, the method comprising:outputting a direct current (“DC”) power signal from a power supply andsupplying the DC power signal that is output from the power supply tothe radio over a power cable; measuring a voltage of the DC power signalat a radio end of the power cable that is remote from the power supply;communicating information regarding the measured voltage of the DC powersignal at the radio end of the power cable to the power supply; andadjusting a voltage level of the DC power signal that is output from thepower supply in response to the information regarding the measuredvoltage of the DC power signal at the radio end of the power cable tomaintain the DC power signal at the radio end of the power cable at asubstantially constant voltage notwithstanding variation in a currentlevel of the DC power signal, wherein the substantially constant voltagecomprises a voltage that exceeds a nominal power signal voltage of theradio and which is less than a maximum power signal voltage of theradio, and wherein the substantially constant voltage is closer to amaximum power signal voltage of the radio than the substantiallyconstant voltage is to the nominal power signal voltage.
 12. The methodof claim 11, wherein the substantially constant voltage is within 4Volts of the maximum power signal voltage of the radio.
 13. The methodof claim 11, wherein the substantially constant voltage is at least 4Volts above the nominal power signal voltage of the radio and less thanthe maximum power signal voltage of the radio.